In a gas chromatograph apparatus, a liquid sample is injected into a sample vaporizing chamber, and the vaporized sample is carried on a carrier gas and is introduced into a column. At this time, a total flow volume f of the carrier gas to be supplied to a sample introducing part needs to be controlled precisely for accurate quantitative determination and quantitative determination in an analysis, and thus the total flow volume f of the carrier gas in a carrier gas supply flow channel is measured by using a pressure difference sensor and a pressure sensor (for example, see Patent Document 1).
FIG. 3 is a schematic configuration diagram illustrating an example of a gas chromatograph apparatus of the related art.
A gas chromatograph apparatus 101 includes a sample vaporizing chamber 10 in which a sample is injected and vaporized, a column 11, a detector 12, a carrier gas supply flow channel 20, a purge flow channel 30, a split flow channel 40, a control unit 150, and a flow controller 160.
A septum formed of silicon rubber (not illustrated) is fitted in an opening provided at a head portion of the sample vaporizing chamber 10. An outlet end of the carrier gas supply flow channel 20 for introducing the carrier gas, an inlet end of the purge flow channel 30 for discharging outside undesired components generated in the septum, an inlet end of the split flow channel 40 for discharging outside an excessive vaporized sample together with the carrier gas, and an inlet end of the column 11 are connected to an interior of the sample vaporizing chamber 10. At the time of the analysis using the sample vaporizing chamber 10 as described above, an analyst is capable of dropping a liquid sample into the interior of the sample vaporizing chamber 10 by picking a needle of a microsyringe 13 having a liquid sample stored therein into the septum. As the septum has a resiliency, a hole formed when the needle is inserted is closed immediately when the needle is removed.
The carrier gas supply flow channel 20 includes, from an upstream side, a cylinder 14 containing the carrier gas encapsulated therein, a laminar flow tube (flow channel resistance) 21 configured to cause an adequate pressure drop in the carrier gas, and a control proportional valve (control valve) 24 configured to be capable of adjusting an opening degree for adjusting the total flow volume f of the carrier gas disposed therein. Further provided are a pressure sensor (pressure detecting portion) 22 configured to detect a supply pressure pin on an upstream side of the laminar flow tube 21 and a pressure difference sensor (pressure difference detecting portion) 23 configured to detect a pressure difference Δp between a supply pressure pin on the upstream side of the laminar flow tube 21 and a pressure on a downstream side thereof.
The purge flow channel 30 includes a pressure sensor 31 configured to detect an inlet port pressure pe, an openable and closable purge valve 32, and a pressure sensor 33 configured to detect a purge pressure pp, and the split flow channel 40 includes an openable and closable discharge valve 41 disposed thereon. Therefore, when the inlet port pressure pe in the sample vaporizing chamber 10 abruptly increases, the discharge valve 41 is opened to discharge a certain ratio of the carrier gas or the sample in the sample vaporizing chamber 10 to the outside via the split flow channel 40.
The control unit 150 is embodied by a personal computer and includes a CPU 151 and a memory (storage part) 152. Describing functions processed by the CPU 151 with reference to a block diagram in FIG. 3, the CPU 151 includes an acquiring part 51a configured to acquire a supply pressure Pin from the pressure sensor 22 and a pressure difference Δp from the pressure difference sensor 23 at predetermined time intervals, a measuring part 151b configured to measure the total flow volume f of the carrier gas in the carrier gas supply flow channel 20 at the predetermined time intervals, and a flow rate control part 151c configured to control the flow controller 160 based on the obtained total flow volume f and the like.
In the measurement by using the gas chromatograph apparatus 101 as described above, the carrier gas of the total predetermined flow volume f is supplied to the sample vaporizing chamber 10. When the liquid sample is dropped into the interior of the sample vaporizing chamber 10, the sample vaporized in the sample vaporizing chamber 10 is sent to the column 11 together with the carrier gas, and is separated into components in the column 11.
Subsequently, a measuring method for measuring the total flow volume f of the carrier gas by the measuring part 151b of the gas chromatograph apparatus 101 will be described. This measuring method includes a creating process (A′) for creating a common calibration curve of the flow controller 160, a mounting process (B′) for mounting the flow controller 160 to the gas chromatograph apparatus 101, and a calculating process (C′) for calculating the total flow volume f based on the common calibration curve.
(A′) Creating Process
Designers control the supply pressure Pin to a set supply pressure Pin,ref (for example, 600 kPa) by using the flow controller 160 at a predetermined atmospheric pressure P′ref, and then measure a measured total flow volume F1 when the pressure difference Δp is set to a pressure difference ΔP1 by controlling the control proportional valve 24. Furthermore, the designers measure a measured total flow volume F2 when the pressure difference Δp is set to a pressure value ΔP2 by controlling the control proportional valve 24. In this manner, the designers measure respective measured total flow volumes Fn at various pressure differences ΔPN with the supply pressure pin being controlled to the set supply pressure Pin, ref at the predetermined atmospheric pressure P′ref. Then, the designers create the common calibration curve indicating a correlation between the pressure difference Δp and a total flow volume ftemp.
(B′) Mounting Process
The designers mount the flow controller 160 on the gas chromatograph apparatus 101, and store the common calibration curve in the memory 152. In other words, the common calibration curve is used for all the units irrespective of differences among units (gas chromatograph apparatus).
(C′) Calculating Process
At the time of sample analysis performed by analysts, the measuring part 151b calculates a provisional total flow volume ftemp by substituting the pressure difference Δp detected by the pressure difference sensor 23 into the common calibration curve. Subsequently, the measuring part 151b obtains the total flow volume f by substituting the supply pressure pin detected by the pressure sensor 22, the provisional total flow volume ftemp, and the set supply pressure Pin,ref into the following expression (4).f=ftemp×(pin/Pin,ref)  (4)